Display screen or portion thereof with a graphical user interface for a test platform



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface for a test platform, showing our new design.

The outermost broken-line perimeter in the FIGURE illustrates the display screen or portion thereof and forms no part of the claimed design. The remaining broken lines in the drawing illustrate portions of the graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface for a test platform, as shown and described. 